The present invention relates to a process for the single-stage imaging and developing or decoating of reproduction layers in an aqueous electrolyte solution.
Radiation-sensitive (photosensitive) reproduction layers are used, for example, in the preparation of offset printing plates and in the preparation of photoresists (both referred to hereinafter as copying materials). In general, such layers are applied to a support by the customer or industrial manufacturer. The layer supports used in such copying materials include metals, such as zinc, magnesium, chromium, copper, brass, steel, silicon, aluminum or combinations of these metals; plastic films; and paper or similar materials. These supports can be coated with the radiation-sensitive reproduction layer without a surface modifying pretreatment of the support, but preferably the coating step is preceded by surface modification such as mechanical, chemical and/or electrochemical roughening, surface oxidation and/or treatment with agents which impart hydrophilicity (for example in the case of supports for offset printing plates).
In addition to at least one radiation-sensitive compound, conventional reproduction layers also usually contain an organic binder (resins or the like) and, optionally, plasticizers, pigments, dyestuffs, surfactants, sensitizers, adhesion promoters, indicators and other customary additives. In order to produce an image from the reproduction layers, the layers are developed after their exposure (irradiation) to obtain, for example, a printing form or a photoresist. In the case of electrophotographic layers, the step of decoating corresponds to the developing step. Within the framework of this invention, the term "reproduction layers" also includes layers which do not contain a radiation-sensitive compound but which contain the other above-mentioned components, in particular an organic binder.
European Patent Application No. 0,073,445 (equivalent to South African Pat. No. 82/5879) discloses a process for developing irradiated reproduction layers, in which those parts of the layer which correspond to the non-image areas are removed with an aqueous electrolyte solution by an electrochemical treatment. The solution employed in particular has a pH in the range from 2.0 to 10.0 and contains at least one salt in a concentration from 0.1% up to the saturation limit of the solution of the particular salt. The electrolyte may furthermore contain a surfactant in a concentration of 0.1% to 5%. In this process, there is, however, required a separate irradiation step prior to development.
Processes have also been described by which it is possible to produce a printing form without an irradiation and/or developing step and thus without use of the customary reproduction layers containing a radiation-sensitive compound. Processes of this type are, for example, known from:
German Pat. No. 24 33 448 (corresponding to U.S. Pat. No. 4,086,853), which describes the use of an electro-responsive recording blank comprising (a) a hydrophobic underlayer (for example, comprised of polyester), (b) an electrically conductive hydrophilic layer (for example, comprised of aluminum) arranged thereon, which can be locally removed by the action of current applied via a stylus, and (c) a layer (for example, comprised of a cellulose derivative, a plasticizer and a pigment) which, as a result of the action of electric current, can be removed from layer (b);
German Offenlegungsschrift No. 25 14 682 (corresponding to British Pat. No. 1,490,732), which describes the use of an electro-responsive recording material comprising (a) an electrically conductive oleophilic layer (for example, comprised of aluminum) which cannot be removed by the action of electric current and (b) an oleophobic silicone rubber layer arranged thereon which can be locally removed by the action of current by means of a stylus;
European Patent Application No. 0,030,642, which describes a process for producing, by electro-erosion, a printing form from a sheet-like material which comprises (a) a hydrophobic substrate layer (for example, of polyester), (b) a hydrophilic, electrically conductive intermediate layer (for example, of aluminum) and (c) a protective dielectric top layer (for example, of Al.sub.2 O.sub.3), in which process both layers (c) and (b) are removed by the action of electrodes.
It is true that printing forms can be produced using these processes, but it is impossible with such forms to achieve long print runs. Moreover, their practical use is considerably restricted by the materials comprising the hydrophilic and hydrophobic areas, or the oleophobic and oleophilic areas, of the printing form, respectively, e.g., with regard to the printing machines, chemicals, inks and/or paper that can be employed.